Pattern formation method for electroluminescent element

ABSTRACT

There is provided a pattern formed object having an electroluminescent layer coating. The pattern formed object comprising a substrate, partition walls provided on the substrate, and a coating stacked on the substrate in its part between the partition walls, wherein the partition walls have a sloped liquid non-repellent surface and have a section form that, at least in the lower part of the partition wall, as the distance from the substrate increases, the size of the partition wall in a direction parallel to the substrate decreases, and in the coating, the ratio of the maximum thickness (Tmax) to the minimum thickness (Tmin), Tmax/Tmin, is not more than 130% as measured in the coating in its part between the lower ends of the partition walls adjacent to each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/980,273 filed on Oct. 30, 2007 (now U.S. Pat. No.7,898,173), which is a divisional application of Ser. No. 10/630,089filed on Jul. 30, 2003 (now U.S. Pat. No. 7,307,381), which claims thebenefit of Japanese serial number 2002-222296, filed Jul. 31, 2002 andJapanese serial number 2002-230899 filed Aug. 8, 2002. The disclosuresof each of the above applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an electroluminescent (EL) display anda process for producing the same.

2. Background Art

(1) First Aspect of the Invention

In recent years, flat displays have become used in various fields andplaces, and advance in information technology has rendered flat displaysmore and more important. At the present time, liquid crystal displays(LCDs) are representative flat displays. The development of organic ELs,inorganic ELs, plasma display panels (PDPs), light emitting diodedisplays (LEDs), vacuum fluorescent displays (VFDs), field emissiondisplays (FEDs) and the like as flat displays based on a displayprinciple different from that of LCDs are also being energetically made.All of these novel flat displays are displays called self-luminescenttype. These self-luminescent displays are greatly different from LCDs inthe following points and have excellent properties not

LCDs are displays called photoreception type. Liquid crystal per se doesnot emit light and functions as the so-called shutter for permitting thetransmission of external light or cutting off the external light toconstitute a display. Due to this nature of the liquid crystal, LCDsrequire the use of a light source, generally backlight. On the otherhand, self-luminescent displays per se emit light, and, thus, there isno need to provide a separate light source for emitting light. In thephotoreception-type displays like LCDs, backlight is always in a lightedstate regardless of the mode of information displayed, and powerconsumption consumed in non-display state is substantially the same asthat in wholly display state. On the other hand, in the self-luminescentdisplays, power is consumed only in sites necessary for lightingdepending upon display information. Therefore, the power consumption isadvantageously smaller than that of the photoreception-type displays.

Further, in LCDs, since a dark state is provided by cutting off lightfrom the backlight, it is difficult to completely prevent light leakage.On the other hand, in the self-luminescent displays, non-luminescentstate is the dark state. Therefore, an ideal dark state can easily beprovided, and, thus, the self-luminescent displays are also muchsuperior to LCDs in contrast.

In LCDs, since polarized light control by taking advantage ofbirefringence of liquid crystals is utilized, the display state greatlyvaries depending upon the direction of viewing. That is, the displaystate is highly dependent upon the view angle. On the other hand,self-luminescent displays are substantially free from this problem.

Further, in LCDs, since a change in orientation derived from dielectricanisotropy of liquid crystals as an organic elastic substance isutilized, theoretically, the time of response to an electric signal isnot less than 1 ms. On the other hand, in the above new technology ofwhich the development is being forwarded, electrons/holes, that is,carrier transition, electron release, plasma discharge and the like areutilized. Therefore, the response time is on the order of ns, that is,is much higher than the response speed of LCDs, and, thus, theself-luminescent displays are free from a problem of after image ofmoving images attributable to the slow response speed of the LCDs.

Among the self-luminescent displays, organic ELs have been particularlyenergetically studied. Organic ELS are also called “OEL” or “organiclight emitting diode (OLED).”

An OEL element and an OLED element have such a construction that a layercontaining an organic compound (EL layer) is interposed between a pairof electrodes, an anode and a cathode. A fundamental structure of thiselement is a laminate structure of “anode electrode/hole injectionlayer/luminescent layer/cathode electrode” proposed by Tang et al.(Japanese Patent No. 1526026). Tang et al. Japanese Patent No. 1526026uses a low-molecular material. On the other hand, Nakano et al. JapanesePatent Laid-Open No. 273087/1991 uses a high-molecular material.

Further, an attempt to use a hole injection layer or an electroninjection layer has been made to improve efficiency. Furthermore, anattempt to dope a luminescent layer with a fluorescent dye or the likehas been made to control colors of emitted light.

The construction of an EL element is generally such that an EL layer isformed on an anode provided for each pixel and a cathode is provided asa common electrode on the EL layer. In this case, the thickness of theanode is large and is about 200 nm from the viewpoint of loweringelectric resistance. The EL layer having a small thickness of 30 to 150nm is formed on the thick anode. Therefore, disadvantageously, breakingof the EL layer occurs on the side face of the anode. Breaking of the ELlayer disadvantageously causes shortcircuiting between the anode and thecathode in the broken part. This makes it impossible to exhibitluminescence of the EL layer, and black point defects are formed. In theprior art technique, when the EL layer is formed by the vapordeposition, the thickness of the EL layer in its part located at theboundary between the partition wall and the electrode is smaller thanthe other parts, and current concentration occurs in this part. In orderto solve the problem involved in the prior art technique, that is, theproblem of electrode breaking and the problem of the smaller thicknessof the EL layer in its part located at the boundary between thepartition wall and the electrode, in Yamazaki et al. Japanese PatentLaid-Open No. 164181/2002, as shown in FIGS. 10 and 11, the upper ends300, 400 of tapered partition walls are convexly curved in sectionrelative to the substrate, and the lower ends 301, 401 of the taperedpartition walls are concavely curved in section relative to thesubstrate. This construction is described to have solved the problem ofelectrode breaking and the problem of uneven layer thickness.

The present inventor has made experiments using partition walls proposedin the Yamazaki et al. publication. As a result, it was confirmed thatthe problem of electrode breaking did not occur. However, when the ELlayer was formed by an ink jet method, as shown in FIG. 12, the problemof uneven layer thickness became more significant. The reason for thisis probably that a liquid reservoir phenomenon occurs in the concavelycurved part in the lower end 301 and, due to this phenomenon, attractionof the EL layer ink to the side face of the partition wall is enhanced.

The formation of the EL layer by a wet process has many advantages andis a promising method for the preparation of an organic EL display.However, except for the following complicated Inoue's process, there wasno method for evenly controlling the layer thickness. A well-knownmethod for the preparation of an organic EL display is one described inInoue: “Kara Porima EL Disupurei (Color Polymer EL Display),” Vol. 22,No. 11, O plus E, p. 1433-1440. In this method, as shown in FIG. 5,partition walls 4 are formed on an insulating layer 8. An luminescentmaterial 5 in an ink form is ejected through an ink jet nozzle 9 to putthe luminescent material 5 selectively on a pixel opening 6 (FIG. 15).In order to fix the ink of the luminescent material, the pixel openingand the insulating layer are treated to impart hydrophilic nature. Theinsulating layer is provided for preventing insulation failure betweenthe opposed electrodes caused by electric field concentration at theedge of the electrode, that is, interelectrode leak. Further, as shownin FIG. 5, the partition walls are subjected to waterrepellency-imparting treatment so that ink droplets not ejected on thepixel opening but impacted on the partition wall are allowed to flow inthe pixel opening.

Fujita et al. Japanese Patent Laid-Open No. 351787/2001 proposes anorganic EL element having partition walls similar to the partition wallsdescribed in Yamazaki et al. document. The partition wall has a footpart having a triangle-, trapezoid- or arc-like tapered shape around theelectrode, and the foot part is concavely curved. The EL layer is formedby a printing method. What is referred to in the Fujita et al.publication is electrode breaking at the lower ends 301, 401 in theYamazaki's display, and the Fujita et al. publication is silent on theevenness of the layer thickness. FIGS. 2(a), (b) and (c) in JapanesePatent Laid-Open No. 351787/2001, however, shows the bulged shape of theEL layer along the side face of the partition wall. Thus, the problemsto be solved by the present invention remain unsolved.

Under these circumstances, the present invention has been made, and anobject of the present invention is to provide an organicelectroluminescent display having excellent practicality that can beproduced by a simple method which does not cause electrode breaking andcan realize even thickness of an electroluminescent layer.

(2) Second Aspect of the Invention

An electroluminescent (EL) element includes a pair of opposedelectrodes. A luminescent layer containing an organic fluorescentcoloring matter, optionally together with other layers such as a holeinjection layer, is interposed between the pair of electrodes. In thisEL element, upon recombination of electrons and holes provided in theluminescent layer, energy is generated. The energy excites the phosphorin the luminescent layer to emit light. In the EL element, a reductionin thickness and a reduction in weight can be realized. Further, the ELelement has high brightness and is also suitable for the display ofmoving images. Therefore, the development of EL elements for variousdisplay applications have been forwarded.

In a general EL element, in general, three types of luminescent layersdifferent from one another in color of luminescence should be regularlyarranged. To this end, various methods have been studied. A currentlycommonly employed method is to form the luminescent layer by an ink jetmethod using a coating liquid for luminescent layer formation. In orderto prevent the formation of the luminescent layer in an area other thanthe predetermined area, a partition wall is provided between adjacentpixels so that the coating liquid for the formation of a luminescentlayer, which exhibits luminescence of a specific color, is applied onlyin the inside of a space surrounded by the partition walls.

Japanese Patent Laid-Open No. 323276/2000 discloses a pattern formedobject as shown in FIG. 27. Specifically, a partition wall 1014 formedof a photosensitive polyimide or the like is provided between pixelelectrodes 1013 of ITO film or the like provided on a transparentsubstrate 1012. The assembly is subjected to continuous plasma treatmentof oxygen gas plasma and fluorocarbon gas plasma to render the surfaceof the electrode hydrophilic and to render the surface of the partitionwall 1014 water-repellent. Both a hole injection layer and a luminescentlayer are formed by an ink jet method to form a pattern formed object(an element) 1011. Since, however, the surface of the partition wall1014 of polyimide has been rendered water-repellent, upon theapplication of the coating liquid by the ink jet method, the partitionwall 1014 repels the coating liquid 1015. Therefore, as shown in FIG.27A, the application of the coating liquid 1015 in its center part is ina bulged state. Thus, a coating (a luminescent layer) 1015′, in whichthe center of the pixel is in a bulged state, is formed. In this coating(luminescent layer) 1015′ (FIG. 27B), the concentration of an electricfield occurs in a relatively thin layer part. This leads to a drawbackthat only the peripheral part of the luminescent layer along thepartition wall exhibits luminescence.

Japanese Patent Laid-Open No. 351787/2001 discloses that the part aroundthe partition wall, in which the luminescent layer is not formed, can besignificantly reduced by providing partition walls having a tapered footpart in which the surface of the foot part is concavely curved insection. In the formation of the partition walls, however, although onlysome description on materials for black matrix (chromium and resin blackare described as an example; and a resist is used in the workingexample) is found, there is no specific description on the formation ofthe unique shape in the foot part of the partition wall. Therefore,reproduction of the partition wall is difficult.

Japanese Patent Laid-Open No. 148429/2002 discloses that, when thepartition walls are subjected to both roughening treatment (to provideRa about 3 to 50 nm) and plasma treatment using fluorineelement-containing gas, the ink adhesion can be improved by the formertreatment to reduce the level of bulge and, thus, it is possible toprovide such a sectional form that the level of bulge of the center partis small, the height of the peripheral part is high, and the layerthickness other than that of the peripheral part is uniform. However, inaddition to the fact that the bulge in the center part is not fullyremoved, the height of the coating at the peripheral part becomes large.Therefore, a part, located somewhat inward from the peripheral part, hasa smaller layer thickness. Further, since the maximum layer thicknessand the minimum layer thickness are within ±25% of the average layerthickness, disadvantageously, for example, only a part near thepartition wall exhibits luminescence, or otherwise luminescence isexhibited only in a narrowed region.

Further, in the above methods described in Japanese Patent Laid-OpenNos. 323276/2000 and 148429/2002, since the partition walls areliquid-repellent, a hole injection layer, which is in many casesprovided together with the luminescent layer, is less likely to beevenly formed. Unlike the luminescent layer, in the formation of thehole injection layer, there is no need to change color of luminescencefor each pixel, and the hole injection layer may be formed on the wholearea.

Accordingly, an object of the present invention is to provide a patternformed object having a coating as an electroluminescent layer or thelike having even thickness, for an electroluminescent element, formedusing a coating liquid and provided in each area surrounded by partitionwalls provided on a substrate provided with partition walls.

SUMMARY OF THE INVENTION (1) First Aspect of the Invention

The above object of the present invention can be attained by anelectroluminescent display comprising at least

a substrate,

an electrode provided on the substrate,

protrusions which each are provided on the substrate so as to cover theends of the electrode and are convexly curved in section relatively tothe surface of the substrate, and

an electroluminescent layer provided in each opening which is located onthe electrode and defined by adjacent protrusions.

Further, the present invention provides a process for producing anelectroluminescent display, comprising the step of

forming an organic layer including at least an electroluminescent layeron the surface of the above substrate with protrusions provided thereonby a wet process selected from an ink jet method, a printing method, acasting method, an alternating adsorption method, a spin coating method,a dipping method, and a dispenser method.

Furthermore, the present invention provides an electronic equipmentcomprising the above display as a display part.

According to the present invention, a display having excellentpracticality can be provided by a process, which is simpler than theprior art process, involving the formation of a uniform coating using acoating liquid of an organic electroluminescent material, for example, ahigh-molecular organic electroluminescent material or a coating-typelow-molecular organic electroluminescent material. Further, the presentinvention can provide an electronic equipment having excellentpracticality provided with this display.

(2) Second Aspect of the Invention

As a result of extensive and intensive studies, the present inventor hasfound that the provision of partition walls having sloped side faceslike banks in rivers is advantageous in that, even when the height ofthe surface of the coating as the luminescent layer in its part locatedon the slope of the partition wall is large, the thickness of thecoating in its luminescent part can be made even because the coating inits part located on the partition wall does not exhibit luminescence byvirtue of the positional relationship between the coating and theelectrode. The present invention has been made based on such finding.

Embodiments of the Invention

(1) A pattern formed object comprising:

a substrate;

partition walls provided on the substrate; and

a coating stacked on the substrate in its part between the partitionwalls, wherein

said partition walls have a liquid-nonrepellent surface and have such asectional form that, at least in the lower part of the partition wall,as the distance from the substrate increases, the size of the partitionwall in a direction parallel to the substrate decreases, and

in said coating, the ratio of the maximum thickness (Tmax) to theminimum thickness (Tmin), Tmax/Tmin, is not more than 130% as measuredin the coating in its part between the lower ends of the partition wallsadjacent to each other.

(2) The pattern formed object according to the above item (1), whereinthe angle of the lower part of the partition wall to the substrate isnot more than 60 degrees.

(3) The pattern formed object according to the above item (2), whereineach of the partition walls comprises a lower partition wall structure,which is provided on the substrate side and is in the form of atrapezoid, in section, with the long side being located on the substrateside, and an upper partition wall structure provided on the lowerpartition wall structure.

(4) The pattern formed object according to the above item (3), whereinthe angle of the slope of the lower partition wall structure to thesubstrate is not more than 30 degrees.

(5) The pattern formed object according to the above item (3) or (4),wherein the distance between the lower part of the upper partition wallstructure and the end of the lower partition wall structure on itssubstrate side as measured in a direction parallel to the substrate isnot less than 1 μm.

(6) The pattern formed object according to any one of the above items(3) to (5), wherein the height H₁ of the lower partition wall structureas measured in a direction perpendicular to the substrate and the heightH₂ of the upper partition wall structure satisfy a requirementrepresented by H₂>2×H₁>0.1 μm.

(7) A pattern formed object for an electroluminescent element,comprising the pattern formed object according to any one of the aboveitems (1) to (6), said coating being an EL light emitting layersandwiched between a first electrode and a second electrode.

(8) The pattern formed object for an electroluminescent elementaccording to the above item (7), wherein said EL light emitting layerhas a hole injection layer stacked on its substrate side.

(9) A method for pattern formation, comprising the steps of:

forming, on a substrate, partition walls which have aliquid-nonrepellent surface and have such a sectional form that, atleast in the lower part of the partition wall, as the distance from thesubstrate increases, the size of the partition wall in a directionparallel to the substrate decreases;

applying a coating liquid onto the substrate in its part between thepartition walls adjacent to each other; and

drying and solidifying the coating to form a solidified coating of whichthe ratio of the maximum thickness (Tmax) to the minimum thickness(Tmin), Tmax/Tmin, is not more than 130% as measured in the coating inits part between the lower ends of the partition walls adjacent to eachother.

(10) The method for pattern formation according to the above item (9),wherein said partition wall is formed by forming a lower partition wallstructure, which is provided on the substrate side and is in the form ofa trapezoid, in section, with the long side being located on thesubstrate side, and then forming an upper partition wall structureprovided on the lower partition wall structure.

(11) A method for pattern formation for an electroluminescent element,comprising the steps of:

forming a first electrode on a substrate;

forming partition walls according to the method as defined in the aboveitem (9) or (10);

forming a coating as an EL light emitting layer using a coating liquidfor EL light emitting layer formation according to the method as definedin the above item (9) or (10); and

forming a second electrode on the EL light emitting layer.

(12) The method for pattern formation for an electroluminescent elementaccording to the above item (11), wherein the coating liquid for ELlight emitting layer formation is applied by a dispenser method or anink jet method.

(13) The method for pattern formation for an electroluminescent elementaccording to the above item (11) or (12), wherein, prior to theformation of the EL light emitting layer, a hole injection layer isformed between the partition walls adjacent to each other.

(14) The method for pattern formation for an electroluminescent elementaccording to the above item (11) or (12), wherein, prior to theformation of the EL light emitting layer, a hole injection layer isformed on the whole area of the assembly including the upper surface ofthe partition walls.

According to the present invention, the following effects can beattained.

According to the pattern formed object in the above item (1), since thepartition walls are liquid-nonrepellent, the pattern formed object isfree from a problem that the coating in its center portion is in abulged state. Specifically, as the distance from the substratedecreases, the thickness of the partition wall increases. That is, asthe distance from the substrate increases, the thickness of thepartition wall decreases. Since both sides of the partition wall aresloped, a pattern formed object can be provided in which the occurrenceof uneven thickness of the coating has been prevented.

According to the pattern formed object in the above item (2), inaddition to the effect attained by the above item (1), the occurrence ofthe uneven thickness of the coating can be further effectivelyprevented.

According to the pattern formed object in the above item (3), inaddition to the effect attained by the above item (2), the function ofthe partition wall can be shared between the first partition wallstructure and the second partition wall structure. Therefore, thepattern formed object has an enhanced function.

According to the pattern formed object in the above item (4), since thelower partition wall structure has a more gently sloped surface, theunevenness of the thickness of the coating can be further reduced.

According to the pattern formed object in the above item (5), since thelower limit of the size of the gently sloped surface of the lowerpartition wall structure has been specified, in addition to the effectattained by the above item (3) or (4), the effect of the gently slopedsurface can be further improved.

According to the pattern formed object in the above item (6), since therelationship between the height of the lower partition wall structureand the height of the upper partition wall structure and the lower limitof the absolute value of the height of the lower partition wallstructure and the lower limit of the absolute value of the height of theupper partition wall structure have been specified, the function of thelower partition wall structure and the function of the upper partitionwall structure can be satisfactorily exhibited.

According to the pattern formed object for an electroluminescent elementin the above item (7), the coating as the EL light emitting layer isinterposed between the first and second electrodes. By virtue of thisconstruction, in addition of the effect attained by any one of the aboveitems (1) to (6), a problem can be solved that, based on the coatinghaving even thickness, the luminescent layer within each of thepartition walls partially exhibits luminescence without luminescence inthe whole luminescent layer.

According to the pattern formed object for an electroluminescent elementin the above item (8), in addition to the effect attained by the aboveitem (7), an additional effect can be attained by the coating as the ELlight emitting layer provided with the evenly formed hole injectionlayer.

According to the method for pattern formation for an electroluminescentelement in the above item (9), after liquid-nonrepellent partition wallsare formed, a coating liquid is applied to a portion between thepartition walls, Therefore, the coating formed between the partitionwalls is free from a problem that the coating in its center portion isin a bulged state. Specifically, as the distance from the substratedecreases, the thickness of the partition wall increases. That is, asthe distance from the substrate increases, the thickness of thepartition wall decreases. Therefore, in this method, uneven thickness ofthe coating is less likely to occur.

According to the method for pattern formation in the above item (10), inaddition to the effect attained by the above item (9), the function ofthe partition wall can be shared between the first partition wallstructure and the second partition wall structure. Therefore, thefunction of the partition wall can be enhanced.

According to the method for pattern formation for an electroluminescentelement in the above item (11), in addition to the effect attained bythe above item (9) or (10), the first and second electrodes are formedto interpose the coating as the EL light emitting layer therebetween.Therefore, a problem can be solved that, based on the coating havingeven thickness, the luminescent layer within each of the partition wallspartially exhibits luminescence without luminescence in the wholeluminescent layer.

According to the method for pattern formation for an electroluminescentelement in the above item (12), the coating liquid for EL light emittinglayer formation is applied by a dispenser method or an ink jet method.Therefore, in addition to the effect attained by the above item (10) or(11), the coating liquid can be accurately applied to a portion betweenthe partition walls adjacent to each other.

According to the method for pattern formation for an electroluminescentelement in the above item (13), prior to the formation of the EL lightemitting layer, the hole injection layer is formed. Therefore, inaddition to the effect attained by the above item (11) or (12), anadditional effect can be attained by the EL light emitting layerprovided with the hole injection layer.

According to the method for pattern formation for an electroluminescentelement in the above item (14), the hole injection layer is formed onthe whole area of the assembly including the upper surface of thepartition walls. Therefore, in addition to the effect attained by theabove item (11) or (12), an additional effect can be attained by the ELlight emitting layer provided with the hole injection layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the construction of a displayin an embodiment of the present invention;

FIG. 2 is an enlarged cross-sectional view showing the construction of adisplay in an embodiment of the present invention;

FIG. 3 is an enlarged cross-sectional view showing the construction of adisplay in another embodiment of the present invention;

FIG. 4 is a cross-sectional view showing the construction of aconventional display;

FIG. 5 is a cross-sectional view showing the construction of aconventional display;

FIG. 6 is a cross-sectional view showing the construction of aconventional display;

FIG. 7 is a front view illustrating luminescence in pixels in displayusing a conventional display;

FIG. 8 is a cross-sectional view showing the construction of anotherconventional display;

FIG. 9 is a front view illustrating luminescence in pixels in displayusing the conventional display shown in FIG. 8;

FIG. 10 is a cross-sectional view showing the construction of animproved conventional display;

FIG. 11 is a cross-sectional view showing the construction of anotherimproved conventional display;

FIG. 12 is a cross-sectional view showing the construction of animproved conventional display produced by a wet process;

FIG. 13 is a cross-sectional view showing the construction of an organicelectroluminescent element;

FIG. 14 is a cross-sectional view showing the construction of anotherorganic electroluminescent element;

FIG. 15 is a diagram illustrating a production method of an organicelectroluminescent display by an ink jet method;

FIG. 16 is a circuit diagram showing the construction of a pixel in anactive drive organic electroluminescent display;

FIG. 17 is a diagram showing the construction of matrix pixels in anactive drive organic electroluminescent display;

FIG. 18 is a front view showing an example of the arrangement of pixelsin a display according to the present invention;

FIG. 19 is a front view showing another example of the arrangement ofpixels in a display according to the present invention;

FIG. 20 is a front view showing a further example of the arrangement ofpixels in a display according to the present invention;

FIG. 21 is an embodiment of an electronic equipment provided with thedisplay according to the present invention;

FIG. 22 is a scanning electron photomicrograph of the cross section of adisplay in an embodiment of the present invention;

FIG. 23 is a scanning electron photomicrograph of the cross section of adisplay in another embodiment of the present invention;

FIG. 24 is a diagram showing a pattern formed object in which partitionwalls having a single layer structure are provided;

FIG. 25 is a diagram showing a pattern formed object in which partitionwalls having a two layer structure are provided;

FIG. 26 is a diagram showing an example of the application of a patternformed object to an electroluminescent element;

FIG. 27 is a diagram showing a conventional pattern formed object;

FIG. 28 is a diagram showing a process up to the step at which partitionwalls are formed in the production process of the present invention;

FIG. 29 is a diagram showing a process up to the step at which anelectroluminescent element is formed.

FIGS. 30A and 30B are diagrams of an EL element with partition wallsformed therein in Example B1;

FIGS. 31A and 31B are diagrams of an EL element with first partitionwalls formed therein in Example B2; and

FIGS. 32A and 32B are diagrams of an EL element with first and secondpartition walls formed therein in Example B2.

In FIGS. 1 to 32,

1: display part, 2: substrate, 3: electrode, 4: partition wall, 5: ELlayer, 6: opening, 7: counter electrode, 8: insulating layer, 9: nozzle,10: luminescence, 11: scanning line G, 12: data signal line D, 13: powersupply line V, 14: switching TFT, 15: gate holding capacitor, 16: ELdrive TFT, 17: EL element, 18: pixel, 19: operating part, 20: equipment,21: lens, 1001: pattern formed object (EL element), 1002: substrate,1003: electrode (1031: first electrode, 1032: second electrode), 1004:partition wall (1004 a: lower partition wall structure, 1004 b: upperpartition wall structure), 1005: coating liquid (1005′: coating), 1051:coating liquid for hole injection layer formation (1051′: hole injectionlayer), 1052-1054: coating liquid for luminescent layer formation(1052′-1054′: luminescent layer), and 1006: mask pattern.

DETAILED DESCRIPTION OF THE INVENTION (1) First Aspect of the Invention

Embodiments of the present invention will be described with reference tothe accompanying drawings.

FIG. 1 is a cross-sectional view showing the construction of a displayin an embodiment of the present invention, FIG. 2 an enlargedcross-sectional view showing the construction of a display in anembodiment of the present invention, and FIG. 3 an enlargedcross-sectional view showing the construction of a display in anotherembodiment of the present invention.

In forming an electroluminescent layer by an ink jet recording method, acommonly employed method is to eject dots of an electroluminescentmaterial ink for each pixel. Thus, pixels arranged as shown in FIG. 18are formed. In this case, the electroluminescent layer is formed on asubstrate provided with an electrode and a partition wall. FIGS. 1, 2,and 3 are cross-sectional views taken on line A-B or C-D of FIG. 18.

When an electroluminescent layer is formed so that a plurality of pixelsadjacent to each other emit the same color, for example, in data linesin a passive matrix display, as well as in data lines even in an activematrix display in a striped pixel arrangement, the sameelectroluminescent color may be adopted. In this case, as shown in FIG.19, the opening of the partition wall is also formed in a line form, andthe electroluminescent layer may be formed by an ink jet recordingmethod or alternatively may be formed by the so-called dispenser method.

In the formation of the electroluminescent layer by the ink jetrecording method using ink solutions, the shape of pixels is alsoimportant. When the pixels to be formed have a corner part as shown inFIGS. 18 and 19, there is a tendency that the ink solution cannot forman accurate corner part but a broken corner. Therefore, as shown in FIG.20, the opening of the pixel is preferably in an elliptical or circularform which does not have any corner part so that surface tension actsevenly. More preferably, the partition wall is formed in this way.

In the present invention, a pixel electrode and a counter electrodeconstitute a pair of electrodes, any one of which is an anode and theother a cathode. All layers provided between the pair of electrodes arecollectively called “EL layer.” The EL layer includes the hole injectionlayer, the hole transport layer, the electroluminescent layer, theelectron transport layer, and the electron injection layer as describedabove.

FIG. 13 is a cross-sectional view showing the structure of an organic ELelement.

Organic EL emits light upon the application of an electric field acrosselectrodes to allow current to flow in the EL layer. The prior arttechnique utilizes only fluorescence caused upon a transition from asinglet excited state to a ground state. Recent research, however, hasrealized effective utilization of phosphorescence caused upon atransition from a triplet excited state to a ground state. This hascontributed to a considerable improvement in luminescence efficiency.

The organic EL is generally produced by forming a light transparentelectrode 3 on a light transparent substrate 2, such as a glasssubstrate or a plastic substrate, and then forming an EL layer 5 and acounter electrode 7 in that order. In many cases, the anode is a lighttransparent electrode formed of ITO or the like, and the cathode is alight non-transparent electrode formed of a metal.

The organic EL element undergoes a significant deterioration inproperties upon exposure to moisture or oxygen. To cope with this and toensure reliability, a method is adopted wherein, in order to avoid theexposure of the element to moisture or oxygen, in general, the elementis filled with inert gas while using another substrate (not shown inFIG. 13), or the so-called sealing is carried out by thin filmdeposition (not shown in FIG. 13).

As with LCDs, displays using organic EL elements can be classifiedroughly into a passive matrix system and an active matrix systemaccording to electrode construction and driving methods. In the passivematrix system, a pair of electrodes are constituted by a horizontalelectrode and a vertical electrode which sandwich the EL layertherebetween and cross each other. The passive matrix system isadvantageously simple in structure, but on the other hand, for thedisplay of images, the instantaneous brightness should be enhanced bytime division scanning by a value obtained by multiplying the brightnessby the number of scanning lines. In a display having better performancethan conventional VGA, an instantaneous brightness exceeding 10,000cd/m² is required of organic EL, and, thus, the display involves manypractical problems. On the other hand, in the active matrix system, apixel electrode is formed on a substrate with TFT or the like formedthereon, and an EL layer and a counter electrode are then formed. Theactive matrix system is advantageous as an organic EL display in variouspoints, for example, in terms of luminescence brightness, powerconsumption, and crosstalk, although the active matrix system has a morecomplicated structure than the passive matrix system.

Further, in the case of active matrix displays using a polycrystallinesilicon (polysilicon) film or a continuous grain boundary silicon (CGsilicon) film, the charge mobility in the polysilicon film or the CGsilicon film is higher than that in an amorphous silicon film.Therefore, heavy current processing of TFT is possible, and this rendersthe active matrix system suitable for driving organic EL which is acurrent drive element. Further, in polysilicon TFT and CG silicon TFT,high-speed operation is possible. Therefore, unlike the prior arttechnique in which processing was carried out by external IC, variouscontrol circuits and display pixels may be provided on an identicalsubstrate. This can offer various advantages such as a size reduction indisplay, a reduction in cost, and realization of multifunctions.

FIG. 16 is a diagram showing the construction of a typical pixel circuitof an active matrix organic EL display. The pixel circuit includes ascanning line G 11, a data signal line D 12, each bus line of a powersupply line V 13 and, further, switching TFT 14, a gate holdingcapacitor 15, driving TFT 16, and an EL element 17. A gate of theswitching TFT selected by the scanning line G is opened, and a signalvoltage corresponding to luminescence intensity is applied to a TFTsource through the data signal line D. This permits the gate of thedriving TFT to be analogically opened according to the level of thesignal voltage, and this state is held in the gate holding capacitor.Upon the application of voltage through the power supply line V to asource of the driving TFT, a current corresponding to the degree ofopening of the gate is allowed to flow in the EL element. As a result,luminescence takes place in a gradation manner depending upon the levelof the signal voltage. FIG. 17 is a diagram showing the construction ofan actual active drive organic EL display in which 18 pixels are arrayedin a matrix form.

For organic EL displays, additional circuit constructions and drivingmethods include digital gradation driving methods, for example, aconstruction using an increased number of TFTs (Yumoto et al.:“PixEL-Driving Methods for Large-Sized Poly-Si AM-OLED Displays,” AsiaDisplay/IDW, '01 p. 1395-1398); time division gradation (Mizukami etal.: “6-bit Digital VGA OLED,” SID, '00 p. 912-915); and area divisiongradation (Miyashita et al.: “Full Color Displays Fabricated by Ink-JetPrinting,” Asia Display/IDW, '01 p. 1399-1402). In the presentinvention, any of these techniques may be used.

Also for the passive matrix system, in the case of a simple displaywhich is small in the number of scanning lines, a practical device canbe realized by utilizing the simple structure. Further, the developmentof phosphorescence emitting materials in addition to conventionalfluorescence emitting materials has been forwarded. By virtue of this,the luminescence efficiency has been significantly improved. Theutilization of these materials, which can realize high luminescenceefficiency, leads to a possibility that conventional problems involvedin the passive matrix system can be solved.

As shown in FIG. 14, studies on a top emission structure, in whichluminescence 10 is taken out from the electroluminescent element in itsside remote from the substrate, is also being forwarded. Against the topemission structure, the structure shown in FIG. 13 is sometimes called“bottom emission structure.” In the top emission structure particularlyin an active matrix display, the luminescent area ratio is not limitedby circuit construction such as TFT and bus line, and more functionaland complicated circuits can be formed. Therefore, the development ofthe top emission structure is being forwarded as a promising techniquefor future applications.

In the present invention, any of the above techniques may be used inorganic EL.

Methods for achieving color display include: a three-color juxtapositionmethod wherein organic EL materials for three primary colors, R, G, andB, are accurately arranged for each pixel in a display; a CF methodwherein a white luminescent layer and color filters (CF) for threecolors of R, G, and B are combined; and a CCM (color changing medium)method wherein a blue luminescent layer and fluorescence conversion dyefilter for R and G are combined.

The methods for achieving color display will be compared. In the CFmethod, a white electroluminescent material is necessary. Regarding thewhite electroluminescent material, apparent white organic EL materialsfor lighting applications have been realized. However, true whiteorganic EL materials with a spectrum of three colors of R, G, and B havenot been realized yet. Further, since color filters are used, theutilization of luminescence is disadvantageously reduced to one-third ofthe utilization of luminescence in the case where no color filter isused.

In the CCM method, since only a blue electroluminescent material isused, the luminescence efficiency and the efficiency of conversion to Rand G by the CCM filter are important. Since, however, satisfactoryefficiency cannot be achieved without difficulties, the CCM method hasnot yet been put to practical use. In CF-type LCDs, the reproduction oftelevision video images is difficult. In the electroluminescent display,as with the CF-type LCDs, the CF method is unsatisfactory in colorreproduction. The CCM method is also a kind of filter method and thus isunsatisfactory in color reproduction. On the other hand, in thethree-color juxtaposition method, superior color reproduction isprovided by subtly regulating the composition of electroluminescentmaterials of individual colors. Overall, the three-color juxtapositionmethod is more advantageous than the CF method and the CCM method,because, in the CF method and the CCM method, due to the use of colorfilters, for example, the thickness of the element is large and thenumber of necessary components is large.

When low-molecular materials are used, the three-color juxtaposed finepixels are formed by vacuum deposition with a mask. On the other hand,in the case of high-molecular materials, solutions are preparedtherefrom, and the three-color juxtaposed fine pixels are formed by anink jet method or other printing method or by a transfer method. Inrecent years, coatable low-molecular materials have also been developed.

In color displays using the three-color juxtaposition method, the vacuumdeposition of the low-molecular material with a mask is disadvantageousin that meeting a demand for an increase in size is difficult due tolimitations on a vacuum device and a mask for vapor deposition and, inaddition, the preparation of a large number of displays using largesubstrates is difficult. This means that the vacuum deposition of alow-molecular material with a mask poses no problem in the preparationof prototype electroluminescent displays in a development stage, but onthe other hand, in a full-scale production stage, it is difficult tomeet the request of the market from the viewpoints of tact and cost. Onthe other hand, in high-molecular materials and coatable low-molecularmaterials, a film can be formed by a wet process such as ink jetting,printing, casting, alternating adsorption, spin coating, or dipping.Therefore, the above problem of coping with large substrates is notsignificant. In particular, the ink jetting can realize the preparationof high-definition displays and thus can be said to be the mostpromising method for future applications.

In the vacuum deposition using a mask, in selectively placing theelectroluminescent material on the pixel part, the major part of theelectroluminescent material is deposited on the mask. As a result,disadvantageously, the utilization of the electroluminescent material issignificantly lowered.

On the other hand, the ink jet method is a method with the highestmaterial utilization, because the electroluminescent material can beselectively disposed only on the required pixel part.

Methods for preparing an organic EL display by an ink jet method will bedescribed.

A well-known ink jet method is described in Inoue: “Kara Porima ELDisupurei (Color Polymer EL Display),” Vol. 22, No. 11, O plus E, p.1433-1440. According to this method, a partition wall 4 is formed on aninsulating layer 8 as shown in FIG. 5. An electroluminescent material 5in an ink form is ejected through an ink jet nozzle 9 and is selectivelydeposited on a pixel opening 6 (FIG. 15). In order to fix theelectroluminescent material ink onto the pixel opening and theinsulating layer, the pixel opening and the insulating layer arepreviously treated to render them hydrophilic. The insulating layer isprovided from the viewpoint of preventing insulating failure betweencounter electrodes caused by field concentration at the edge of theelectrode, that is, the so-called “interelectrode leak.”

A problem involved in the ink jet method is that ink droplets sometimesimpact sites different from the openings as the target sites. What isimportant for placing the electroluminescent material accurately inopenings for a large number of respective pixels is to move inkdroplets, which have impacted sites different from the pixels, to thepixel openings. To this end, in the Inoue's method, as shown in FIG. 5,the partition wall is subjected to water repellency-imparting treatment.More specifically, the electrode is formed from ITO, the insulatinglayer is formed from SiO₂, and the partition wall is formed frompolyimide. After the whole surface of the substrate is once treated O₂plasma to render the whole surface of the substrate hydrophilic, thewhole surface of the substrate is treated with CF₄ plasma. The treatmentwith CF₄ plasma renders only the polyimide partition wallwater-repellent, whereby a desired substrate surface state is realized.Even after the treatment with CF₄ plasma, the surface of the ITOelectrode and the surface of SiO₂ insulating layer maintain thehydrophilicity.

When the partition wall is formed of an insulator, as shown in FIG. 4,the partition wall can serve also as the insulating layer. In this case,the number of steps can be advantageously reduced. In the Inoue'smethod, however, this is not possible. In order that ink droplets, whichhave impacted sites different from the pixels, are moved to andaccurately fixed to the pixel opening, as shown in FIG. 4, the adoptionof a method, wherein the partition wall is rendered water-repellentwhile the electrode is rendered hydrophilic, is considered effective. Inthis case, however, a part of the electrode is exposed in a boundarybetween the partition wall and the electrode, and, as a result, aninterelectrode leak disadvantageously occurs between the electrode andthe counter electrode.

On the other hand, a method is known wherein the partition wall is notrendered water-repellent to avoid the cissing of the El layer in theboundary between the partition wall and the electrode, thereby realizingan organic EL display not involving the problem of the interelectrodeleak. In the Inoue's method, the height of the partition wall is about 2μm, while, in this method, the height of the partition wall ispreferably not less than 5 μm from the viewpoint of allowing inkdroplets for the EL layer to surely impact the pixel opening. In thedrawing, the height of the partition wall is indicated by a character H.Why the height of the partition wall in this method should be largerthan the height of the partition wall in the Inoue's method is that, inthe Inoue's method, the flow of the ink for the EL layer into sitesdifferent from the target pixel opening is prevented by taking advantageof the water repellency of the partition wall, whereas, in the abovemethod, the flow of the ink for the EL layer into sites different fromthe target pixel opening is prevented by taking advantage of the largeheight of the partition wall. The utilization of the partition wallhaving large height, however, poses various different problems.

In order to eliminate the cissing of the ink for the EL layer at theboundary between the partition wall and the electrode, as shown in FIG.6, a certain level of hydrophilicity should be imparted to the side faceof the partition wall to hold the ink for the EL layer on the side faceof the partition wall. As described above in connection with the Inoue'smethod, a polyimide or the like, which is easy to be patterned, is usedfor the formation of the partition wall. Acrylic resins, photosensitiveresists and the like may also be used. These materials are in many casesgenerally hydrophilic so far as they are originally water-repellent orare not subjected to special water repellency-imparting treatment aspost treatment. When the partition wall is formed of these materials,the partition wall can easily hold the ink for the EL layer on the sideface thereof and thus can eliminate cissing of the ink for the EL layerat the boundary between the partition wall and the electrode. In thiscase, however, the formation of the so-called “meniscus” surface stateis unavoidable due to surface tension of the liquid caused by theholding of the ink for the EL layer on the side face of the partitionwall. When the coating is dried by evaporation of the solvent from theink for the EL layer while maintaining the meniscus surface shape, themeniscus surface shape in the form of ink as such is reflected. As aresult, as shown in FIG. 6, the thickness of the EL layerdisadvantageously becomes uneven. Upon the application of an electricfield to the EL layer having uneven thickness, current is concentratedin a smaller thickness portion while satisfactory current does not flowin a larger thickness portion. As a result, a different in luminescencebrightness occurs between the smaller thickness portion and the largerthickness portion. Actually, as shown in FIG. 7, the application of anelectric field to the EL layer having uneven thickness as shown in FIG.6 causes such an unfavorable phenomenon that luminescence takes place inonly the center portion of the pixel having a smaller thickness. FIG. 7shows the case where the pixel opening is rectangular and the case wherethe pixel opening is elliptical. Luminescence only in the center portionof the pixel as shown in FIG. 7 cannot provide satisfactory brightnessand efficiency as a display.

A problem of breaking of the counter electrode is also important. Thecounter electrode is generally formed by vapor deposition of a thinmetal film. Therefore, the thickness of the metal film which can bestably formed is 100 to 500 nm. A film having a thickness of more than500 nm is not a thin film, and, in this case, there is an increasingtendency that the film is turned up by the action of the tension of themetal per se and is peeled off. In the above defined film thicknessrange, when the height of the partition wall is not less than 5 μm, asshown in FIG. 6, breaking is likely to occur in the corner part of thepartition wall. This leads to the occurrence of a large number ofdefective pixels in which an electric field is not applied to the ELlayer.

A conventional technique for solving this problem is to adopt a taperedshape in the partition wall as shown in FIG. 8. Also in this case,however, the problem of breaking of the electrode cannot be fullysolved. Japanese Patent Laid-Open No. 164181/2002 (Yamazaki et al.)describes that, when the EL layer is formed by vapor deposition, thethickness of the EL layer is small in a boundary part 202 between thepartition wall and the electrode and current is concentrated in thispart. In this case, as shown in FIG. 9, contrary to the phenomenon shownin FIG. 7, luminescence takes place only around pixels. Also in thiscase, the brightness and the efficiency of the display are notsatisfactory. In order to solve the problems involved in the use of theconventional partition wall structure, that is, the breaking of theelectrode and the reduction in thickness of the EL layer at the boundarybetween the partition wall and the electrode, Yamazaki has adopted acurved shape as shown in FIGS. 10 and 11 in the upper ends and the lowerends of the partition wall. Specifically, as shown in FIGS. 10 and 11,the upper ends 300, 400 of the tapered partition wall are convexrelative to the substrate, and the lower ends 301, 401 of the taperedpartition wall are concave relative to the substrate. This can realizean organic EL display which has solved the problems of electrodebreaking and uneven film thickness.

Equipment on which the display provided by the present invention ismounted as a display part 1 includes those 20 as shown in FIG. 21, forexample, a portable telephone (a cellular phone) and PDA (personaldigital assistant) type terminals provided with an operating part 19,PCs (personal computers), television sets, video cameras, and digitalcameras.

(2) Second Aspect of the Invention

Both FIGS. 24 and 25 are cross-sectional views showing typicalstructures of the pattern formed object according to the presentinvention.

As illustrated in FIG. 24, a pattern formed object 1001 according to thepresent invention includes pixel-shaped electrodes 1003 provided on thesubstrate 1002 while providing a space therebetween. For example, apartition wall 1004, which is trapezoidal in section, is providedbetween the electrodes 1003. In this case, the long side of thetrapezoid is located on the substrate 1002 side. The partition wall 1004covers a part of the end of each of the left and right electrodes 1003.A coating 1005′, formed by coating a coating liquid 1005 and drying andsolidifying the coating, is stacked between the partition walls 1004.

Preferably, both sides of the partition wall 1004 constitute an up-gradeslope as viewed from the substrate 1002 side. The inclinations of bothsides may be the same or different. When a large number of partitionwalls 1004 are provided on the substrate 1002, however, the sameproperties are required of both sides of the partition wall. Therefore,the sectional form of the partition wall 1004 is preferably bilaterallysymmetrical relative to a direction perpendicular to the substrate 1002in the drawing. The sectional form of the partition wall is not limitedto a trapezoid, and may be, for example, an isosceles triangle. In theaccompanying drawing, the electrode 1003 (1013 in the case of the priorart) is drawn thick for clear understanding. In fact, however, theelectrode 1003 is very thin and is negligible relative to the dimensionof the height or the like of the partition wall. Therefore, theunderside of the partition wall 1004 (surface on the substrate 1002side) is flat independently of the sectional form shown in the drawing.

The slope of both sides of the partition wall 1004 is not preferablysteep and does not have a large gradient close to the right angle to thesubstrate. As shown in FIG. 24A, the angle θ₁ relative to the substrate1002 (or relative to the electrode 1003 provided parallel to thesubstrate 1002) is preferably not more than 60 degrees. When both sidesof the partition wall 1004 have this inclination, it is possible tosuppress such an unfavorable tendency that, upon drying andsolidification of the coating liquid 1005 to form a coating 1005′, thecoating 1005′ in its part around the partition wall 1004 rises along thepartition wall and the height of that part defined as the distancebetween the surface of the coating 1005′ and the substrate 1002 islarger than the other parts. The θ₂ may be very small and may be notmore than 60 degrees. When the θ₂ is excessively small, the width of thepartition wall 1004 (dimension of the partition wall in a directionparallel to the substrate 1002) is excessively large. For this reason,the θ₂ is preferably not less than 30 degrees.

Even when both sides of the partition wall 1004 are in the aboveinclined state, it is impossible to completely prevent the unfavorablephenomenon in which the height of the coating 1005′, defined as thedistance between the surface of the coating and the substrate 1002, inits part around the partition wall 1004 is larger than the other parts.Even though the unfavorable phenomenon cannot be completely prevented,as shown in FIG. 26A, in the case of an EL element in which the coating1005′ is provided as a luminescent layer and an electric field isapplied to a portion between the lower electrode 1003 and the upperelectrode 1003′ provided on the coating 1005′ to cause luminescence, thecoating 1005′ in its portion provided on both sides of the partitionwall 1004 is off the top of the electrode 1003 and thus is notluminescent. The difference in thickness of the coating 1005′ betweenthe thicker part in the left and right sides of the coating except forthe part located on the partition wall 1004 and the thinner part locatedin the center part of the coating 1005′ is not significant and thus hasno significant influence.

In the prior art technique described in Japanese Patent Laid-Open No.148429/2002, the partition wall should have a slope necessarilyincluding a concave face in its base part. According to studiesconducted by the present inventor, so far as both sides of the partitionwall are in a gently inclined state, uneven thickness of the coating1005′ in its part around the partition wall can be eliminated. Even whena part of the slope of both sides of the partition wall is located onthe electrode, uniform luminescence can be easily realized in thecoating 1005′, because the coating 1005′ in its part located on thepartition wall is not luminescent even when the thickness of that partis somewhat different from that of the other parts. That is, preferably,the slope of the partition wall begins at least at an end of theelectrode, more preferably at a position on the electrode.

In the above embodiment, the partition wall 1004 has a single layerstructure. Alternatively, the partition wall 1004 may have a two layerstructure of a lower layer and an upper layer. Specifically, a two layerstructure of a partition wall lower structure 1004 a and a partitionwall upper structure 1004 b as shown in FIG. 25 may be adopted. In thepartition wall lower structure 1004 a, the sectional form istrapezoidal, and the long side of the trapezoid (as described above, thethickness of the electrode 1003 being negligible) is on the substrate1002 side. The left and right sides of the partition wall cover the endsof the electrode 1003. The partition wall upper structure 1004 b isstacked on the partition wall lower structure 1004 a. As shown in FIG.25, the partition wall upper structure 1004 b may be in such atrapezoidal sectional form that the long side of the trapezoid lookstoward the partition wall lower structure 1004 a side, and the length ofthe long side is substantially equal to the length of the short side inthe cross section of the partition wall lower structure 1004 b.Alternatively, the sectional form of the partition wall upper structure1004 b may be in the form of an isosceles triangle or in the form of acircular form. Further, both sides of the partition wall upper structure1004 b may be parallel to each other.

When the partition wall 1004 has the above two layer structure, theslope of the inclined plane in the partition wall lower structure 1004 amay be smaller than the slope θ₁. The reason for this is as follows.When the partition wall 1004 has a single layer structure and at thesame time, θ₁ is small, the coating 1005 is not applied to an area otherthan the predetermined area. In this case, an attempt to increase theheight of the partition wall 1004 requires increasing the width(dimension in the left and right direction in the drawing) of thepartition wall 1004. Therefore, as a whole, this constitutes an obstacleto the formation of a fine pattern.

On the other hand, in the two layer structure, even when the gradient θ₁of the slope on both sides in the partition wall lower structure 1004 ais relatively small and is not more than 30 degrees, the height of thewhole partition wall 1004 can be increased by increasing the height ofthe partition wall upper structure 1004 b. Further, since the gradientθ₁ of the slope on both sides in the partition wall lower structure 1004a can be reduced, an increase in thickness of the coating 1005′ in itssurface located on the partition wall lower structure 1004 a relative tothe substrate 1002 can be suppressed. The height of the coating 1005′ inits part around the partition wall upper structure 1004 b relative tothe substrate is of course large. This part, however, is outside the topof the lower electrode. Therefore, as shown in FIG. 26B, in the case ofan EL element in which the coating 1005′ is provided as a luminescentlayer and an electric field is applied to a portion between the lowerelectrode 1003 and the upper electrode 1003′ provided on the coating1005′ to cause luminescence, the coating in its part having largerheight is not luminescent and thus does not have any adverse effect. Thepartition wall lower structure 1004 a and the partition wall upperstructure 1004 b preferably satisfy a requirement H₂>2×H₁>0.1 μm whereinH₁ represents the height of the partition wall lower structure 1004 aand H₂ represents the height of the partition wall upper structure 1004b. In this case, both the function of the partition wall lower structure1004 a and the function of the partition wall upper structure 1004 b canbe satisfactorily exhibited. The height of the partition wall lowerstructure 1004 a is preferably not less than 0.05 μm. When the height ofthe partition wall lower structure 1004 a is below the lower limit ofthe above defined height range, upon the application of an electricfield to a portion between the upper and lower electrodes 1003 and 1003′in an EL element produced using this structure, there is a fear that theinsulating property cannot be maintained. A larger height of thepartition wall lower structure 1004 a is more advantageous in theapplication of the coating liquid 1005. When the resultant patternformed object 1001 is utilized as an EL element, an excessively largeheight of the partition wall lower structure 1004 a influences thethickness of the EL element. Therefore, the height H₁ of the partitionwall lower structure 1004 a and the height H₂ of the partition wallupper structure 1004 b preferably satisfy a relationship represented byformula H₂>2×H₁.

The angle θ₁, which is the gradient of the slope of both sides of thepartition wall lower structure 1004 a in the partition wall 1004, can bereduced to a very small value. In an extreme case, the θ₁ may be 0(zero) degree. In this case, the partition wall upper structure 1004 bmay be such that a thin plate is provided perpendicularly to thesubstrate 1002 and the angle to the substrate is not more than 90degrees. Ultimately, the partition wall 1004 may be of such a sectionalform that “T” formed by joining two straight lines to each other hasbeen inverted. In fact, however, the partition wall lower structure 1004a has a larger height in its center part than the other part from theviewpoints of the preparation of the partition wall and the maintenanceof insulation from the electrode. Therefore, the θ₁ value is preferablynot less than 5 degrees, more preferably not less than 10 degrees, froma practical viewpoint. In any event, since the gradient of the slope inthe partition wall lower structure 1004 a may be relatively small, ingeneral, the partition wall lower structure can be easily formed using acommonly used resist composition.

In Japanese Patent Laid-Open No. 148429/2002 described above inconnection with the prior art technique, there is a description to theeffect that the partition wall may be either a single layer structure ora multilayer structure. This publication, however, is silent on theabove-described multilayer structure in a specific form.

The size of the partition wall lower structure 1004 a in its slope parton which the partition wall upper structure 1004 b is not stacked, thatis, the size of the slope part as measured in a direction parallel tothe substrate 1002 (Δa in FIG. 25B), is preferably not less than 1 μm.When the size is not less than 1 μm, the coating 1005′ in its parthaving larger height relative to the substrate 1002 than the other partcan be constructed to have no influence on luminescence. For the samereason, also in the partition wall 1004 having the above single layerstructure, the size of the slope of the partition wall 1004 in adirection parallel to the substrate 1002 is preferably not less than 1μm. The size of the partition wall 1004 (or the partition wall lowerstructure 1004 a) in its part provided on the electrode 1003 is alsopreferably not less than 1 μm.

In the pattern formed object 1001 according to the present invention,the adoption of the partition wall 1004 having the above structure cansuppress uneven thickness of the coating 1005′. The ratio of the maximumthickness Tmax to the minimum thickness Tmin in the coating 1005′, thatis, Tmax/Tmin, is preferably not more than 130%. As shown in FIGS. 24Band 25B, the minimum thickness Tmin of the coating 1005′ is measured ina portion around the center of the coating 1005′ provided betweenadjacent partition walls 1004. On the other hand, as shown in FIGS. 24Band 25B, the maximum thickness Tmax of the coating 1005′ is measured atboth ends of the coating in which the electrode 1003 is not covered withthe partition wall 1004 and is exposed. Tmax/Tmin is preferably not lessthan 100%.

The pattern formed object 1001 according to the present invention hasbeen described, while quoting FIGS. 26A and 26B, to be usable as an ELelement. When the use of the pattern formed object 1001 according to thepresent invention as the EL element is contemplated, other layers suchas a hole injection layer may be provided. The hole injection layer maybe interposed between the electrode 1003 on the substrate 1002 and thecoating 1005′ as the luminescent layer.

The pattern formed object 1001 according to the present invention can beproduced by forming the above partition wall 1004 on the substrate 1002,applying a coating liquid to a portion between the partition walls anddrying and solidifying the coating. When the partition wall 1004 to beformed has a two layer structure, the partition wall 1004 is formed in atwo-stage process. When the pattern formed object 1001 is used as an ELelement, prior to the formation of the partition wall 1004, an electrodeis sometimes formed on the substrate 1002. Further, in some cases, inthe application of the coating liquid 1005, a method is adopted whereina composition for hole injection layer formation is applied to form ahole injection layer and a composition for luminescent layer formationis then applied to form a luminescent layer. Further, when the patternformed object 1001 is used as the EL element, the formation of theluminescent layer is followed by the formation of an electrode differentfrom the above formed electrode. The production process of the patternformed object 1001 according to the present invention as an EL elementand materials used for the production process will be described withreference to FIGS. 28 and 29. The present invention is suitable for theapplication to an EL element. Further, the present invention is suitablyapplicable to products, other than EL elements, where partition walls ina lattice form or the like are provided and a part between the partitionwalls is colored, for example, color filters in which the partition wallis in a black matrix form.

The substrate 1002 of the pattern formed object 1001 is in a plate orfilm form. Materials usable for constituting the plate or the filminclude inorganic materials such as glass and quartz or resin plates andfilms. The term “substrate” as used herein is used as including a plate-or film-shaped material and may be used interchangeably with the term“backing” or “base.” When the substrate 1002 is a resin film, a flexibleproduct, which can be rolled or bent, can be provided.

As shown in FIG. 28A, a first electrode 1031 is provided on thesubstrate 1002. The first electrode 1031 is formed of, for example, atransparent conductive layer and is in many cases formed of a thin filmof indium tin oxide (ITO), indium oxide, gold, polyaniline or the like.After the thin film is evenly formed on the whole surface of thesubstrate, the formation of a resist pattern followed by etching canprovide the first electrode 1031 having a desired shape.

The electrode stacked on the substrate 1002 is called a first electrode,and the electrode stacked on the EL layer is called a second electrode.The first and second electrodes may be formed on the whole surface ofthe substrate, or alternatively may be formed in a pattern form on thesubstrate. Preferably, any one of the first and second electrodes is ananode, and the other a cathode. Further, preferably, any one of thefirst and second electrodes is transparent or semi-transparent.Preferably, the anode is formed of a conductive material having a largework function which enables holes to be easily injected, and the cathodeis formed of a conductive material having a small work function whichenables electrons to be easily injected. Preferably, both the first andsecond electrodes are formed of a material having the lowest possibleelectric resistance. A metallic material is generally used.Alternatively, an organic material or an inorganic compound may be used.

Specific examples of anode materials usable for constituting the firstand second electrodes include indium tin oxide (ITO), indium oxide,gold, and polyaniline. Specific examples of cathode materials includemagnesium alloys, for example, MgAg, aluminum alloys, for example, AlLi,AlCa, and AlMg, and metallic calcium. For both the anode material andthe cathode material, a mixture of a plurality of materials may be used.

A partition wall 1004 is formed on the substrate 1002, with the firstelectrode 1031 formed thereon, at its parts between first electrodepatterns. The partition wall 1004 may be formed by thick layer printing.Alternatively, the partition wall 1004 may be formed as follows. Asillustrated in FIG. 28, a coating liquid containing a photosensitiveresin is coated onto the whole surface of a substrate 1002 with a firstelectrode 1031 provided thereon (FIG. 28B) to form a coating 1004 a. Thecoating 1004 a is then subjected to patternwise exposure, for example,by placing a mask pattern for exposure and patternwise exposing thecoating 1004 a to light (FIG. 28C). After the patternwise exposure, thecoating 1004 a is developed with a predetermined developing solution toform partition walls 1004 in their parts between first electrodepatterns (FIG. 28D). If necessary, heat curing may be carried out (FIG.28E).

Accordingly, the partition wall 1004 may be formed of a cured product ofa photosensitive resin. Alternatively, the partition wall may be formedof a cured product of a resin curable upon exposure to an ionizingradiation including an electron beam, a cured product of a thermosettingresin, or a thermoplastic resin. Independently of the type of resinconstituting the partition wall 1004, preferably, the partition wall1004 is formed of a material not containing any liquid repellentcomponent, that is, is formed of a liquid-nonrepellent material or isnot liquid-repellent at least in its surface. When the surface of thepartition wall 1004 is liquid-nonrepellent, it is possible to solve aproblem that, in the formation of a luminescent layer or a holeinjection layer, the luminescent layer or hole injection layer in itspart near the partition wall is subjected to cissing and, consequently,the center portion of the luminescent layer or hole injection layerrises. When a partition wall 1004 having a two layer structure isformed, the above procedure may be repeated twice, or alternatively acombination of different methods may be used.

Methods for making the angle of the partition wall 1004 to the substrate1002 (or to the electrode), i.e., θ₁, small include a method wherein amaterial having relatively low photoresolution is used, a method whereinthe height of the partition wall is increased, a method wherein thethickness of the partition wall is increased, a method wherein, at thetime of exposure, the gap (spacing) between the mask pattern 1006 andthe coating 1004 a is increased, a method wherein the exposure isincreased, a method wherein the development time is increased, and amethod wherein higher temperature conditions are adopted for heat curingafter the development.

For example, when the photosensitive positive-working resist ispatternwise exposed, a difference in quantity of light occurs between aportion near the surface of the resist and a deeper portion in theresist and, in addition, an unexposed portion around the exposed portionis also dissolved. Therefore, when the thickness is larger, a wider areanear the surface is dissolved while, in a deeper portion, a smaller areais dissolved, whereby a partition wall 1004 having small θ₁ is provided.In the patternwise exposure, when the gap between the surface of theresist and the mask pattern is increased, the influence of generateddiffracted light extends to a non-opening portion of the mask pattern.Therefore, when the gap is larger, the θ₁ value of the partition wall1004 is smaller. Under conventional exposure conditions in which the gapis not large, the influence of the diffracted light is not substantiallysignificant. Increasing the exposure causes the influence, and, in thiscase, the same effect as attained by increasing the gap can be attained.When the development time is increased, as the position is closer to thesurface of the resist, the period of time for which the developmentsolution acts is longer. The unexposed portion is also dissolved forthis long period of time. Therefore, as with the case where thethickness of the resist is large, a partition wall 1004 having small θ₁is provided. Alternatively, upon heating of the resist after thedevelopment, the sectional form is broken and becomes gently sloped,because the positive-working resist has low heat resistance.

The angle θ₁ can be regulated in the range of 5 to 90 degrees by varyingthe above conditions for rendering θ₁ small and, if necessary, combiningtwo or more conditions.

Next, in the substrate 1002 with the first electrode 1031 and thepartition walls 1004 formed thereon, a coating liquid 1051 for holeinjection layer formation is applied to a portion between partitionwalls 1004 (FIG. 29F). The coating liquid for hole injection layerformation may be applied by a dispenser method wherein the coatingliquid is dropped by means of a suitable dispenser for each portionbetween the adjacent partition walls, or by an ink jet method.Alternatively, the coating liquid may be applied by the so-called “spincoating” wherein the coating liquid is dropped on a suitable position onthe substrate 1002 and the substrate 1002 is then rotated at a highspeed to spread the coating liquid. The applied coating liquid 1051 forhole injection layer formation is heated by heat treatment such asvacuum heat treatment to form a hole injection layer 1051′.

Materials usable for constituting the hole injection layer (or the anodebuffer material) include phenylamine compounds, star burst-type aminecompounds, phthalocyanine compounds, oxides such as vanadium oxide,molybdenum oxide, ruthenium oxide, and aluminum oxide, amorphous carbon,polyaniline, and polythiophene derivatives.

For example, an aqueous solution ofpoly(3,4)ethylenedioxythiophene/polystyrene sulfonate (abbreviated toPEDOT/PSS, manufactured by Bayer; tradename: Baytron P AI 4083;commercially available as an aqueous solution) commercially available asa composition for hole injection buffer formation may also be used asthe coating liquid for hole injection layer formation. The holeinjection layer may also be formed of an alternate adsorption multilayerfilm.

In the production process of the pattern formed object according to thepresent invention, in dropping a coating liquid in a portion between thepartition walls 1004 by means of a dispenser or in applying the coatingliquid by an ink jet method, when the partition wall 1004 has a slope,since the opening on which the coating liquid is applied is wide, thetolerance of the control of the position of dropping by means of adispenser or the control of the position of the application of thecoating liquid by the ink jet method can be advantageously increased.

In the production process of the pattern formed object according to thepresent invention, the partition wall 1004 at least in its surface ispreferably liquid-nonrepellent. When the partition wall 1004 at least inits surface is liquid-nonrepellent, particularly in applying the coatingliquid 1051 for hole injection layer formation, the coating liquid 1051is less likely to cause cissing from the partition wall 1004. Therefore,advantageously, even a method which can evenly coat the coating liquidonto a relatively wide area, such as a spin coating method, can beutilized. When the partition wall 1004 is liquid-repellent, it isdifficult to adopt a process for forming a hole injection layer on thewhole surface of the substrate, such as a spin coating method. In thiscase, just at the time when the coating liquid 1051 for hole injectionlayer formation is placed on the whole surface of the substrate, thecoating liquid causes cissing from the partition wall 1004 and cannot beevenly coated without difficulties. Even if the coating liquid can becoated by any method, the hole injection layer (in many cases, havinghydrophilic nature) is very likely to stay on the partition wall 1004.In this case, there is a fear of the liquid repellency being lost.

The height of the partition wall 1004 is preferably larger than thelevel of the applied coating liquid for hole injection layer formation,because the partition wall 1004 is liquid-nonrepellent. In the prior arttechnique, the partition wall used in this field is liquid-repellent. Inthis case, when the level of the applied coating liquid is larger thanthe height of the partition wall, the coating liquid undergoes cissingfrom the partition wall. As a result, there is no possibility that thecoating liquid applied to the portion between the partition walls passesover the partition wall and overflows into the adjacent area. On theother hand, in the present invention, since the partition wall 1004 isliquid-nonrepellent, when the coating liquid is applied only once, thereis a possibility that the amount of the applied coating liquid issmaller than that in the prior art technique in which liquid repellentpartition walls are utilized. In this case, if necessary, theapplication of the coating liquid may be repeated twice or more. Theabove relationship between the height of the partition wall and thelevel of the coating liquid and the application of the coating liquidtwice or more are not limited to the application of the coating liquidfor hole injection layer formation and are also applied to theapplication of the coating liquid for luminescent layer formation andcoating liquids for other layer formation.

A luminescent layer is formed in a portion between adjacent partitionwalls provided on the substrate 1002 with the hole injection layer 1051′formed thereon. Preferably, the following method is adopted. Forexample, a coating liquid 1052 for a luminescent layer for redluminescence, a coating liquid 1053 for a luminescent layer for greenluminescence, and a coating liquid 1054 for a luminescent layer for blueluminescence are provided and applied respectively to a portion betweena pair of adjacent partition walls, a portion between another pair ofadjacent partition walls, and a portion between a further pair ofadjacent partition walls so that luminescence of different color can beprovided for each luminescent layer (FIG. 29H). Thereafter, the coatingsare heat dried or vacuum dried (optionally with heating) to solidify thecoatings. Thus, a luminescent layer 1052′ for red luminescence, aluminescent layer 1053′ for green luminescence, and a luminescent layer1054′ for blue luminescence are formed (FIG. 29I). In this case,individual spaces defined by partition walls 1004 are coated withrespective coating liquids separately from one another. Therefore,preferably, the coating liquid is dropped by a dispenser or is appliedby an ink jet method. In some cases, an identical coating liquid isapplied to all spaces defined by the partition walls to form luminescentlayers which exhibit luminescence of an identical color. In this case,preferably, the coating liquid is applied by a method, for example, spincoating, which can evenly coat the coating liquid in a relatively widearea.

An EL element layer for luminescence provided between the first andsecond electrodes may consist of a luminescent layer alone, oralternatively may comprise a hole injection layer and a luminescentlayer. Here these two types of EL element layers will be mainlydescribed. The EL element layer, however, is not limited to these typesonly. For example, EL element layers having various layer constructions,for example, an EL element layer comprising a luminescent layer and anelectron injection layer and an EL element layer comprising aluminescent layer, a hole injection layer, and an electron injectionlayer provided in that order, may be adopted.

Materials usable for constituting the luminescent layer may beclassified roughly into coloring matter-type materials, metalcomplex-type materials, and polymer-type materials.

Coloring matter-type materials include cyclopentadiene derivatives,tetraphenylbutadiene derivatives, triphenylamine derivatives, oxadiazolederivatives, pyrazoloquinoline derivatives, distyrylbenzene derivatives,distyrylarylene derivatives, silole derivatives, thiophene cycliccompounds, pyridine cyclic compounds, perynone derivatives, perylenederivatives, oligothiophene derivatives, trifumanylamine derivatives,oxadiazole dimers, and pyrazoline dimers.

Metal complex-type materials include metal complexes having aluminum(Al), zinc (Zn), beryllium (Be), etc. or rare earth metals such asterbium (Tb), europium (Eu) and dysprosium (Dy) as central metals, andoxadiazole, thiadiazole, phenylpyridine, phenyl benzimidazole andquinoline structures, etc. as ligands, and examples of metal complexesinclude quinolinol aluminum complexes, benzoquinolinol berylliumcomplexes, benzoxazole zinc complexes, benzothiazole zinc complexes,azomethyl zinc complexes, porphyrin zinc complexes, and europiumcomplexes.

Polymer-type materials include polyparaphenylene vinylene derivatives,polythiophene derivatives, polyparaphenylene derivatives, polysilanederivatives, polyacetylene derivatives, polyvinyl carbazole, andpolyfluorene derivatives.

Doping materials may be incorporated in the material for constitutingthe luminescent layer. Doping materials include perylene derivatives,coumarin derivatives, rubrene derivatives, quinacridone derivatives,squarium derivatives, porphyrin derivatives, styryl-based colorants,tetracene derivatives, pyrazoline derivatives, decacyclene, andphenoxazone.

The material for constituting the luminescent layer may be dissolved ordispersed in a suitable solvent to prepare a coating liquid forluminescent layer formation. In the present invention, preferably, thecoating liquid for luminescent layer formation, the coating liquid forhole injection layer formation and other applicable coating liquids havea surface tension of not more than 40 dyn/cm, more preferably not morethan 35 dyn/cm. When the surface tension exceeds 40 dyn/cm, thethickness of the coating is likely to become uneven.

A second electrode is formed on the luminescent layer provided on thesubstrate 1002. In principle, materials usable for constituting thesecond electrode may be the same as those described above in connectionwith the first electrode. Examples of preferred materials for the secondelectrode include magnesium alloys such as MgAg, aluminum alloys such asAlLi, AlCa, and AlMg, and metallic calcium.

When the formation of a cathode buffer layer is contemplated, materialsusable for cathode buffer layer formation include aluminum-lithiumalloys, lithium fluoride, strontium, magnesium oxide, magnesiumfluoride, strontium fluoride, calcium fluoride, barium fluoride,aluminum oxide, strontium oxide, calcium, polymethyl methacrylate, andsodium polystyrenesulfonate.

When the formation of an electron injection layer is contemplated, anymaterial may be used without particular limitation so far as thematerial is an electron transport material. Low-molecular electrontransport materials include oxadiazole derivatives, diphenylquinonederivatives, and anthraquinodimethane derivatives. High-molecularelectron transport materials include a dispersion of the abovelow-molecular materials in polymeric binders. Polymeric binders includepolysilane and thiophene oligomers. The electron injection layer may beformed using these materials by vapor deposition or the like in the caseof the low-molecular material or by a conventional wet process in thecase of the high-molecular material.

EXAMPLES

The following examples further illustrate but do not limit the presentinvention.

(1) First Aspect of the Invention Example A1

A coating liquid for organic EL layer formation according to the presentinvention was prepared according to the following formulation.

(Preparation of Coating Liquid for Organic EL Layer Formation

Polyvinylcarbazole  70 pts. wt. Oxadiazole compound  30 pts. wt.Coumarin 6 (*fluorescent dye)  1 pt. wt. 1,1,2-Trichloroethane (solvent)633 pts. wt *When the fluorescent dye is coumarin 6, green fluorescencehaving a peak at 501 nm is obtained; when the fluorescent dye isperylene, blue fluorescence having a peak at 460 to 470 nm is obtained;and when the fluorescent dye is DCM, red fluorescence having a peak at570 nm is obtained. They were used as luminescent materials forrespective colors.(Preparation of EL Display)

A substrate, with an electrode and a partition wall formed thereon,having a sectional form shown in FIG. 1 was provided. The partition wallcovered the end of the electrode so that the partition wall functionsalso as an electrode insulating layer. The electrode was formed byforming a transparent electrode formed of ITO, a nesa film, IZO or thelike and patterning the transparent electrode by etching. The partitionwall was formed by spin coating a photosensitive resist OFPR-800(viscosity 500 cp) manufactured by Tokyo Ohka Kogyo Co., Ltd. at 1200rpm, prebaking the coating at 110° C., then exposing the coating tolight using a photomask, developing the coating, and post-baking thedeveloped coating at 240° C. The height of the partition wall (layerthickness) formed under the above conditions was 6 μm. The shape of thepartition wall thus formed can be easily observed, for example, under ascanning electron microscope (SEM). Observation under SEM revealed thatthe partition wall was convexly curved in section relative to thesurface of the substrate and that the sectional form comprised a part ofan arc. FIG. 22 shows a scanning electron photomicrograph of the crosssection of the partition wall.

A transparent electrode is used for a bottom emission-type elementstructure. In this case, a transparent substrate is used. A topemission-type element structure may be formed by using a metal in theelectrode. The electrode opening was in a rectangular form having a sizeof 100 μm×300 μm.

After cleaning the substrate, a buffer layer was formed by spin coatingPEDOT/PSS (polythiophene: Bayer CH 8000) having a hole injectionproperty to a thickness of 80 nm and baking the coating at 160° C. Theabove coating liquid for organic EL layer formation was ejected onto thepixel opening on PEDOT by an ink jet method, and the coating was driedat 80° C. to form a 100 nm-thick luminescent layer. Subsequently, anMg(magnesium)-Ag(silver) alloy (Mg:Ag=10:1) was vapor deposited to athickness of 150 nm. Silver (Ag) was then vapor deposited thereon as aprotective layer to a thickness of 200 nm to form a cathode electrode.

When an active matrix display is prepared using a TFT substrate, thecathode electrode is formed on the whole area. On the other hand, when apassive matrix display is prepared, the cathode electrode is formed in astripe form orthogonally to the electrode pattern on the substrate.

Separately, the above procedure was repeated up to the step at which theluminescent layer was formed on the substrate. The substrate wasobserved under SEM and an atomic force microscopy (AFM). As a result, itwas confirmed that, as shown in FIG. 2, in the major part of the pixelopening, the EL layer provided in the pixel opening was flat althoughthe thickness of the EL layer in its part around the boundary 110between the EL layer and the partition wall was slightly larger than theother part of the EL layer. The EL layer in its part around the boundary110 between the EL layer and the partition wall shown in FIG. 2 wasfound to be curved in section in a direction opposite to the curvedsectional form of the partition wall (protrusion) and to be in smoothcontact with the partition wall.

A DC electric field was applied across the electrode for observation ofluminescence in the pixel opening. As a result, unlike luminescenceshown in FIGS. 7 and 9, any luminescence failure derived from uneventhickness of the EL layer did not take place. When a control circuit wasconnected and an image signal was input, a color display with excellentdisplay performance could be provided.

Example A2

The procedure of Example A1 was repeated, except that conditions for thetreatment of the resist material were changed.

Specifically, the same resist material as used in Example A1 was treatedin the same manner as in Example A1, except that the post-bakingtemperature was changed to 180° C. The shape of the partition wall wasobserved under SEM. As a result, as shown in FIG. 3, it was confirmedthat the partition wall was convexly curved in section relative to thesurface of the substrate and that the sectional form of the protrusioncomprised a part of an arc and a flat part located in the upper part ofthe protrusion and extended continuously from the arc part. FIG. 23shows a scanning electron photomicrograph of the cross section of thepartition wall.

Next, an EL display was prepared in the same manner as in Example A1.

Separately, the above procedure was repeated up to the step at which theluminescent layer was formed on the substrate. The substrate wasobserved under SEM and an atomic force microscopy (AFM). As a result, itwas confirmed that, as shown in FIG. 3, in the major part of the pixelopening, the EL layer provided in the pixel opening was flat althoughthe thickness of the EL layer in its part around the boundary 101between the EL layer and the partition wall was slightly larger than theother part of the EL layer. The EL layer in its part around the boundary101 between the EL layer and the partition wall shown in FIG. 3 wasfound to be curved in section in a direction opposite to the curvedsectional form of the protrusion and to be in smooth contact with thepartition wall.

A DC electric field was applied across the electrode for observation ofluminescence in the pixel opening. As a result, unlike luminescenceshown in FIGS. 7 and 9, any luminescence failure derived from uneventhickness of the EL layer did not take place. When a control circuit wasconnected and an image signal was input, a color display with excellentdisplay performance could be provided.

Example A3

The procedure of Examples A1 and A2 was repeated, except that, as shownin FIG. 20, the pixel opening had a shape free from any corner partinstead of the rectangular shape.

In Examples A1 and A2, in the pixel, uniform luminescence could bealmost achieved. When the number of pixels was increased, however, somepixels were defective and the yield of the products was not very high.On the other hand, when the shape of the pixel opening was free from anycorner part, the yield was improved and this pixel opening shape wasmore effective in a practical display of which the number of pixels waslarger than that of VGA.

The present invention has been described with reference to workingexamples. However, it should be noted that the present invention is notlimited to these examples only.

(2) Second Aspect of the Invention

In the preparation of pattern formed objects of examples and comparativeexample, steps up to the step at which a partition wall was formed on asubstrate were carried out as follows.

Example B1

A glass substrate with stripe-shaped transparent ITO electrodes (firstelectrodes) 1031 formed thereon at width: 100 μm and pitch in widthwisedirection: 126 μm (space width: 26 μm) was provided. At the outset, apositive-working photosensitive material (tradename: OFPR-800/800 CP,manufactured by Tokyo Ohka Kogyo Co., Ltd.) was spin coated on the wholesurface of the substrate with ITO electrodes formed thereon to form a 15μm-thick photosensitive resin layer. The photosensitive resin layer wasexposed and developed. After the completion of the development, theresin layer was heat treated at 250° C. for 30 min. As shown in FIG.30A, after registration in such a manner that 5 μm from both ends inwidthwise direction of each stripe-shaped transparent ITO electrode iscovered with the resin layer, openings 1031′ having width: 90 μm, pitchin widthwise direction: 126 μm, length: 300 μm, and spacing inlengthwise direction: 15 μm were formed. As shown in FIG. 30B which is adiagram taken on line A-A of FIG. 30A, the sectional form of partitionwalls formed of a cured product of the photosensitive resin layerremaining unremoved in the formation of the openings was such that thewall was convexly protruded relative to the glass substrate and had wallthickness (size of the wall in its part in contact with the glasssubstrate in widthwise direction in the drawing): 36 μm, height: 12 μm,and angle of both sides of the wall to the glass substrate: 55 degrees.Conditions for providing the angle 55 degrees were previously determinedby a trial and error method. As compared with conventional etching andthe like, the positive-working photosensitive material was applied to alarger thickness, the gap between the mask pattern and the coating atthe time of exposure was made larger, the exposure was larger, and thedevelopment time was longer.

Example B2

In the same manner as in Example B1, a glass substrate with transparentITO electrodes 1031 formed thereon was provided, and a positive-workingphotosensitive material (tradename: TLER P-002PM, manufactured by TokyoOhka Kogyo Co., Ltd.) was spin coated on the whole surface of thesubstrate with ITO electrodes formed thereon to form a 2.5 μm-thickphotosensitive resin layer. The photosensitive resin layer was exposedand developed. After the completion of the development, the resin layerwas heat treated at 250° C. for 30 min. As shown in FIG. 31A, afterregistration in such a manner that 5 μm from both ends in widthwisedirection of each stripe-shaped transparent ITO electrode is coveredwith the resin layer, openings 1031′ having width: 90 μm, pitch inwidthwise direction: 126 μm, length: 300 μm, and spacing in lengthwisedirection: 15 μm were formed. As shown in FIG. 30B which is a diagramtaken on line A-A of FIG. 30A, the sectional form of partition wallsformed of a cured product of the photosensitive resin layer remainingunremoved in the formation of the openings was such that the wall 1004 awas convexly protruded relative to the glass substrate and had wallthickness (size of the wall in its part in contact with the glasssubstrate in widthwise direction in the drawing): 36 μm, height: 2.2 μm,and angle of both sides of the wall to the glass substrate: 15 degrees.The partition walls 1004 a thus formed were designated as firstpartition walls.

The same positive-working photosensitive material as used in Example B1was spin coated on the glass substrate with the first partition walls1004 a formed thereon to form a 12 μm-thick photosensitive resin layer.The photosensitive resin layer was exposed and developed. After thecompletion of the development, the resin layer was heat treated at 250°C. for 30 min. As shown in FIG. 32, second partition walls 1004 b havingwall thickness (size of the wall in its part in contact with the glasssubstrate in widthwise direction in the drawing): 20 μm, total height ofthe first and second partition walls: 12 μm, and angle of both sides ofthe walls excluding the first partition walls 1004 a to the glasssubstrate: 60 degrees were formed on the first partition walls 1004 a.

Comparative Example

In the same manner as in Example B1, a glass substrate with transparentITO electrodes 1031 formed thereon was provided, and a positive-workingphotosensitive material (tradename: PMER P-LA900, manufactured by TokyoOhka Kogyo Co., Ltd.) was spin coated on the whole surface of thesubstrate with ITO electrodes formed thereon to form a 15 μm-thickphotosensitive resin layer. The photosensitive resin layer was exposedand developed. After the completion of the development, the resin layerwas heat treated at 250° C. for 30 min. As shown in FIG. 30A, afterregistration in such a manner that 5 μm from both ends in widthwisedirection of each stripe-shaped transparent ITO electrode is coveredwith the resin layer, openings 1031′ having width: 90 μm, pitch inwidthwise direction: 126 μm, length: 300 μm, and spacing in lengthwisedirection: 15 μm were formed. As shown in FIG. 30B which is a diagramtaken on line A-A of FIG. 30A, the sectional form of partition wallsformed of a cured product of the photosensitive resin layer remainingunremoved in the formation of the openings was such that the wall wasconvexly protruded relative to the glass substrate and had wallthickness (size of the wall in its part in contact with the glasssubstrate in widthwise direction in the drawing): 36 μm, height: 12 μm,and angle of both sides of the wall to the glass substrate: 70 degrees.

The glass substrates with partition walls formed thereon prepared abovewere provided. A commercially available composition for hole injectionbuffer formation (poly(3,4)ethylenedioxythiophene/polystyrene sulfonate(abbreviated to PEDOT/PSS, tradename: Baytron P AI 4083, manufactured byBayer, available as an aqueous solution) was spin coated onto the wholesurface of the substrate on its partition wall side to a thickness of1,000 angstroms.

Thereafter, a 1.0% (by mass) tetralin solution of polyfluorene wasprovided as a composition for organic luminescent material layerformation. The solution was ejected to each portion between adjacentpartition walls by means of an ink jet apparatus in which ink is ejectedby applying voltage to a piezoelectric element. The coatings were thendried in a vacuum heat drier under conditions of temperature: 100° C.and degree of vacuum: 150 mTorr to form a luminescent layer for redluminescence. A thin film of calcium (Ca) having a thickness of 1,000angstroms as a second electrode and a thin film of aluminum (Al) havinga thickness of 2,000 angstroms as a protective electrode were formed inthat order by vacuum deposition on the luminescent layer for redluminescence. Thus, EL elements (=EL light emitting elements) of ExampleB1, Example B2, and Comparative Example were prepared.

The first electrode (ITO) side of the EL light emitting element wasconnected to the positive electrode side, and the second electrode (Ca)side was connected to the negative electrode side. A direct current wasallowed to flow with a source meter, and the luminescent area of thepixel part was observed under an optical microscope. Further, themaximum thickness and the minimum thickness of the luminescent layer forred luminescence within the pixel (corresponding to the exposed portionof the first electrode (ITO)) were measured by observation of the crosssection under SEM. The results are shown in Table 1 below. In Table 1,the luminescent area ratio is the ratio of actually light emitted areato the designed area of the luminescent part.

TABLE 1 Luminescent area Tmax/Tmin, % ratio Example B1 180 0.50 ExampleB2 130 0.80 Comparative Example 115 0.90

1. A method for pattern formation, comprising the steps of: preparing asubstrate on which electrodes are provided with a space between theelectrodes; forming, on the substrate on which the electrodes areprovided in the space between the electrodes, partition walls which havea liquid-nonrepellent surface and have such a sectional form that, atleast in the lower part of the partition wall, as the distance from thesubstrate increases, the size of the partition wall in a directionparallel to the substrate decreases, and the size of the partition wallsin its part provided on the electrode in a direction parallel to thesubstrate is not less than 1 μm; applying a coating comprising an ELlight emitting layer on an upper surface of the electrodes provided onthe substrate in its part between the partition walls; forming the ELlight emitting layer by one of a dispenser method and an ink jet method;and drying and solidifying the coating to form a solidified coating ofwhich the ratio of the maximum thickness (Tmax) to the minimum thickness(Tmin), Tmax/Tmin, is not more than 130% as measured in the coating inits part between the lower ends of the partition walls adjacent to eachother.
 2. The method for pattern formation according to claim 1, whereinsaid partition wall is formed by forming a lower partition wallstructure, which is provided on the substrate side and is in the form ofa trapezoid, in section, with the long side being located on thesubstrate side, and then forming an upper partition wall structureprovided on the lower partition wall structure.
 3. A method for patternformation for an electroluminescent element, comprising the steps of:forming a first electrode on a substrate; forming partition wallsaccording to the method as defined in claim 1; forming a coating as anEL light emitting layer using a coating liquid for EL light emittinglayer formation according to the method as defined in claim 1; andforming a second electrode on the EL light emitting layer.
 4. The methodfor pattern formation for an electroluminescent element according toclaim 3, wherein the coating liquid for EL light emitting layerformation is applied by a dispenser method or an ink jet method.
 5. Themethod for pattern formation for an electroluminescent element accordingto claim 4, wherein, prior to the formation of the EL light emittinglayer, a hole injection layer is formed in a space between the partitionwalls adjacent to each other.
 6. The method for pattern formation for anelectroluminescent element according to claim 4, wherein, prior to theformation of the EL light emitting layer, a hole injection layer isformed on the whole area of the assembly including the upper surface ofthe partition walls.
 7. The method for pattern formation for anelectroluminescent element according to claim 3, wherein, prior to theformation of the EL light emitting layer, a hole injection layer isformed in a space between the partition walls adjacent to each other. 8.The method for pattern formation for an electroluminescent elementaccording to claim 3, wherein, prior to the formation of the EL lightemitting layer, a hole injection layer is formed on the whole area ofthe assembly including the upper surface of the partition walls.